#include<bits/stdc++.h>
#define sd(n) scanf("%d",&n) 
#define sld(n) scanf("%lld",&n)
#define pd(n) printf("%d", (n))
#define pld(n) printf("%lld", n)
#define all(x) (x).begin(),(x).end()
#define rall(x) (x).rbegin(),(x).rend()
#define fi first
#define se second
const int N = 2e5;
const int maxn = 1e6;
#define INF 0x7fffffff
typedef long long int ll;
using namespace std;
//----------------------------------------------------------------------------//
int a[110];
int b[110];
void solve()
{
	int n;
	sd(n);
	int ans = 0;
	for (int i = 1; i <= n; i++) sd(a[i]);

	for (int i = 1; i <= n; i++) b[i] = a[i] + i;

	reverse(b, b + n);
	for (int i = 1; i<n; i++)
	{
		if (b[i]>b[i+1])
		{
			b[i+1] = b[i];
			ans++;
		}
	}

	pd(ans);
	puts("");
}

int main()
{
	int T = 1;
	//sd(T);
	while (T--)
	{
		solve();
	}

	return 0;
}
